The invention relates to a primer, comprising a mixture dissolved or dispersed in one or more solvents, the mixture composed of a copolymer obtained through copolymerization, preferably free-radical copolymerization, of vinylcaprolactam and/or vinylpyrrolidone, and one or more of the following monomers: a) an acrylic acid ester of a linear primary alcohol containing 2 to 10 carbon atoms in the alkyl group of the alcohol, b) an acrylic acid ester of a branched, non-cyclic alcohol having 4 to 12 carbon atoms in the alkyl group of the alcohol, and c) acrylic acid; one or more organofunctional silanes; a dye or a pigment based on a metal complex or a metal oxide, wherein the metal oxide is of a spinel-type. Such primer provide reliable and excellent adhesion between pressure-sensitive adhesive tapes and hydrophilic surfaces, in particular glass, and ensures at the same time a good coloration of the primer, thereby producing an opaque primer layer.